Various artificial lift techniques have been used to improve recovery of oil and/or gas from subterranean reservoirs, such as when production by natural reservoir pressure becomes uneconomical. In particular, plunger lift systems have been effective at improving oil and/or gas recovery in various situations. These systems, for example, often utilize a free-traveling plunger or piston that drops to the bottom of the well. In such systems, also know as free piston systems, as the plunger falls, fluid in the tubing flows around and above the plunger. When desired, one or more wellhead valve is opened, allowing gas in the well to push the plunger up to the surface. As the plunger moves up, liquids above the plunger are pushed to the surface and recovered. This sequence can be repeated by closing the wellhead off and allowing the plunger to fall back into the well.
The ability to produce oil and/or gas from subterranean reservoirs may be enhanced by providing treatment chemicals in the well to reduce viscosity of fluids in the well, corrosion, scale and deposits of undesirable materials, such as paraffin and distillates, in the well or for other purposes. Treatment chemicals can include soap, acid, corrosion inhibitors, scale inhibitors, solvents, dispersants, and inhibitors for paraffin and petroleum distillates, stabilizers, surface active agents and other chemical-based liquids and/or solids.
Various techniques have been employed to deliver treatment chemicals downhole. Some example chemical delivery techniques for use in wells equipped with plunger lift systems are described in U.S. Pat. No. 7,004,258, entitled “Method and Apparatus for Enhancing Oil and Gas Flow in a Well” and issued on Feb. 28, 2006, and U.S. Pat. No. 7,117,947, entitled “Well Chemical Treatment Utilizing Plunger Lift Delivery System” and issued on Oct. 10, 2006.
Existing chemical delivery techniques used in wells equipped with plunger lift systems have limitations. For example, many delivery techniques do not ensure effective delivery of the treatment chemicals to the desired downhole locations. For another example, various existing delivery techniques require the manufacture, installation and effective operation of additional equipment that must be used within the well. For further examples, various existing procedures are uneconomical, unreliable, cumbersome to employ or unsuitable for use in certain wells.
It should be understood, however, that the above-described examples, features and/or disadvantages are provided for illustrative purposes only and are not intended to limit the scope or subject matter of the claims of this patent or any patent or patent application claiming priority hereto. Thus, none of the appended claims or claims of any related patent application or patent should be limited by the above discussion or construed to address, include or exclude the cited examples, features and/or disadvantages, except and only to the extent as may be expressly stated in a particular claim. Further, the above exemplary disadvantages should be evaluated for any particular existing downhole applications on a case-by-case basis.
Accordingly, there exists a need for apparatus and methods useful for providing chemicals into wells equipped with plunger lift systems having one or more of the following attributes, capabilities or features: effectively uses treatment chemicals; minimizes waste of treatment chemicals; assists in providing ideal chemical treatment; assists in ensuring chemicals do not trickle down well or dry up before reaching the well bottom; ensures chemicals are delivered to the well bottom; efficiently delivers chemicals to the desired location in the well; generally uniformly coats the tubing walls with chemicals; provides chemicals into the well quickly at every plunger stroke; repeatedly delivers chemicals to the bottom of the well to prevent scale deposits and/or corrosion; automatically maintains continuous chemical presence in the well; allows nearly continuous treatment of the wellbore; prevents injected chemicals from flowing out of the well with fluid exiting the well; prevents the plunger from preceding chemicals down the well; allows the plunger to be held above the well to allow insertion of chemicals before the plunger drops; allows the plunger to follow the chemicals down the well, pushing chemicals to the bottom, assisting in evenly dispersing chemicals in the borehole or evenly distributing chemicals along the inner surface of the tubing.